Downlink and uplink channel with low latency

ABSTRACT

Certain aspects of the present disclosure provide techniques that may be used to help enable low latency communications between a user equipment (UE) and a base station (BS) using quick uplink channels that enable a reduced transmission time interval (TTI). Additionally, certain aspects of the present disclosure provide techniques for managing communications in a wireless communication system, for example, by using enhanced downlink control channels.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

The present Application is a divisional application of U.S. applicationSer. No. 14/866,465, filed Sep. 25, 2015, which claims benefit of U.S.Provisional Patent Application Ser. Nos. 62/059,726 and 62/059,831, bothfiled Oct. 3, 2014, all of which are herein incorporated by reference intheir entirety.

BACKGROUND I. Field

The present disclosure relates generally to communication systems, andmore particularly, to enhanced downlink control channel designs formanaging communications in a wireless communication system and quickuplink channels that enable a reduced transmission time interval (TTI)for low latency communications.

II. Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier frequency division multiple access (SC-FDMA) systems, andtime division synchronous code division multiple access (TD-SCDMA)systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is Long Term Evolution (LTE). LTE is a set ofenhancements to the Universal Mobile Telecommunications System (UMTS)mobile standard promulgated by Third Generation Partnership Project(3GPP). It is designed to better support mobile broadband Internetaccess by improving spectral efficiency, lower costs, improve services,make use of new spectrum, and better integrate with other open standardsusing OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), andmultiple-input multiple-output (MIMO) antenna technology. However, asthe demand for mobile broadband access continues to increase, thereexists a need for further improvements in LTE technology. Preferably,these improvements should be applicable to other multi-accesstechnologies and the telecommunication standards that employ thesetechnologies.

In wireless communication systems employing legacy LTE, an eNodeB mayreceive data from a plurality of UEs over a shared uplink channel calledthe Physical Uplink Shared Channel (PUSCH). In addition, controlinformation associated with the PUSCH may be transmitted to the eNodeBby the UE via a Physical Uplink Control Channel (PUCCH) and/or anEnhanced PUCCH (ePUCCH).

SUMMARY

Aspects of the present disclosure relate to enhanced downlink controlchannel designs for managing communications in a wireless communicationsystem.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving, in a downlinksubframe comprising two slots, at least one type of advanced physicaldownlink control channel (aPDCCH) from a base station (BS), anddemodulating the aPDCCH based on a cell-specific reference signals(CRSs).

According to certain aspects, the CRSs span one or both of the two slotsin the downlink subframe. In some cases, the method further includesreceiving at least one Physical Downlink Shared Channel (PDSCH) in thedownlink subframe and demodulating the PDSCH based on the CRS.Additionally, the method may include determining a starting symbol ofthe aPDCCH based on signaling from the BS.

In some cases, the aPDCCH is transmitted in a control channel regionthat spans the two slots of the downlink subframe. Additionally, in somecases, the downlink subframe also comprises a data channel region thatspans the two slots of the downlink subframe for carrying Machine TypeCommunication (MTC) data traffic.

According to certain aspects, the aPDCCH comprises a quick physicaldownlink control channel (QPDCCH) having a single-slot transmission timeinterval (TTI) and the QPDCCH is transmitted in a control channel regionthat spans one slot of the downlink subframe. In some cases, the QPDCCHindicates resources, in the same one slot, for a quick physical downlinkshared channel (QPDSCH). Additionally, in some cases, the controlchannel region spans all but a legacy control region of the one slot.According to certain aspects, the downlink subframe further comprisesanother control channel region that spans the two slots of the downlinksubframe and a physical downlink shared channel (PDSCH) region thatspans the two slots of the downlink subframe.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a memorycoupled with at least one processor, wherein the at least one processoris configured to receive, in a downlink subframe comprising two slots,at least one type of advanced physical downlink control channel (aPDCCH)from a base station (BS), and demodulate the aPDCCH based on acell-specific reference signals (CRSs).

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forreceiving, in a downlink subframe comprising two slots, at least onetype of advanced physical downlink control channel (aPDCCH) from a basestation (BS), and means for demodulating the aPDCCH based on acell-specific reference signals (CRSs).

Certain aspects of the present disclosure provide a non-transitorycomputer readable medium for wireless communications. The non-transitorycomputer readable medium generally includes instructions for receiving,in a downlink subframe comprising two slots, at least one type ofadvanced physical downlink control channel (aPDCCH) from a base station(BS), and demodulating the aPDCCH based on a cell-specific referencesignals (CRSs).

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes transmitting, in adownlink subframe comprising two slots, at least one type of advancedphysical downlink control channel (aPDCCH) to a user equipment, andtransmitting cell-specific reference signals (CRS) in the downlinksubframe for the UE to use for demodulating the aPDCCH.

According to certain aspects, in some cases, the CRS spans one or bothof the two slots in the downlink subframe. In some cases, the aPDCCHoccupies resources defined for demodulation reference signals (DMRS) ina legacy control channel when transmitting to certain types of UEs(e.g., MTC UEs).

According to certain aspects, the method further includes transmittingat least one Physical Downlink Shared Channel (PDSCH) in the downlinksubframe to be demodulated by the UE based on CRS. In other aspects, themethod includes signaling an indication of a starting symbol of theaPDCCH to the UE.

According to certain aspects, the aPDCCH is transmitted in a controlchannel region that spans the two slots of the downlink subframe. Insome cases, the downlink subframe also comprises a data channel regionthat spans the two slots of the downlink subframe for carrying MachineType Communication (MTC) data traffic

According to certain aspects, the aPDCCH comprises a quick physicaldownlink control channel (QPDCCH) having a single-slot transmission timeinterval (TTI). In some cases, the aPDCCH is transmitted in a controlchannel region that spans one slot of the downlink subframe.Additionally, in some cases, the control channel region spans all but alegacy control region of the one slot.

According to certain aspects, in some cases, the QPDCCH indicatesresources, in the same one slot, for a quick physical downlink sharedchannel (QPDSCH).

According to certain aspects, the downlink subframe further comprisesanother control channel region that spans the two slots of the downlinksubframe and a physical downlink shared channel (PDSCH) region thatspans the two slots of the downlink subframe.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a memorycoupled with at least one processor, wherein the at least one processoris configured to transmit, in a downlink subframe comprising two slots,at least one type of advanced physical downlink control channel (aPDCCH)to a user equipment, and transmit cell-specific reference signals (CRS)in the downlink subframe for the UE to use for demodulating the aPDCCH.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fortransmitting, in a downlink subframe comprising two slots, at least onetype of advanced physical downlink control channel (aPDCCH) to a userequipment, and means for transmitting cell-specific reference signals(CRS) in the downlink subframe for the UE to use for demodulating theaPDCCH.

Certain aspects of the present disclosure provide a non-transitorycomputer readable medium for wireless communications. The non-transitorycomputer readable medium generally includes instructions fortransmitting, in a downlink subframe comprising two slots, at least onetype of advanced physical downlink control channel (aPDCCH) to a userequipment, and transmitting cell-specific reference signals (CRS) in thedownlink subframe for the UE to use for demodulating the aPDCCH.

Aspects of the present disclosure provide mechanisms for quick uplinkchannels that enable a reduced transmission time interval (TTI) for lowlatency communications.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a user equipment (UE). The method generally includesproviding, to a base station, an indication that the UE is capable ofsupporting low latency communications through one or more quick uplinkchannels, wherein the one or more quick uplink channels enable a reducedtransmission time interval (TTI) for the low latency communicationshaving a shorter duration than a legacy TTI, and performing the lowlatency communications with the base station, using the one or morequick uplink channels, in accordance with the reduced TTI.

According to certain aspects, a duration of the legacy TTI correspondsto a duration of a subframe, wherein the subframe includes two timeslots and the shorter duration of the reduced TTI corresponds to aduration of the time slots. In some cases, the UE is able to transmit aquick physical uplink control channel (QPUCCH) in one, but not both, ofthe two time slots.

According to certain aspects, performing the low latency communicationscomprises transmitting data in a first quick physical uplink sharedchannel (QPUSCH) in one of the time slots.

Additionally, in some cases, the method includes receiving an indicationof whether the data transmitted in the first QPUSCH was successfullyreceived by the base station in a quick physical downlink controlchannel (QPDCCH) transmitted from the base station in accordance withthe reduced TTI. In some cases, the QPDCCH is received during a timeslot a first number of subframes after the QPUSCH transmission inaccordance with the reduced TTI. Additionally, in some cases, theindication in the QPDCCH indicates that the data transmitted in thefirst QPUSCH was not successfully received, and further comprisingretransmitting the data in a second QPUSCH in a time slot a secondnumber of subframes after receiving the indication in the QPDCCH inaccordance with the reduced TTI.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes a memory coupled with at least one processor, whereinthe at least one processor is configured to provide, to a base station,an indication that the UE is capable of supporting low latencycommunications through one or more quick uplink channels, wherein theone or more quick uplink channels enable a reduced transmission timeinterval (TTI) for the low latency communications having a shorterduration than a legacy TTI, and perform the low latency communicationswith the base station, using the one or more quick uplink channels, inaccordance with the reduced TTI.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes means for providing, to a base station, an indicationthat the UE is capable of supporting low latency communications throughone or more quick uplink channels, wherein the one or more quick uplinkchannels enable a reduced transmission time interval (TTI) for the lowlatency communications having a shorter duration than a legacy TTI, andmeans for performing the low latency communications with the basestation, using the one or more quick uplink channels, in accordance withthe reduced TTI.

Certain aspects of the present disclosure provide a non-transitorycomputer readable medium for wireless communications by a user equipment(UE). The non-transitory computer readable medium generally includesinstructions for providing, to a base station, an indication that the UEis capable of supporting low latency communications through one or morequick uplink channels, wherein the one or more quick uplink channelsenable a reduced transmission time interval (TTI) for the low latencycommunications having a shorter duration than a legacy TTI, andperforming the low latency communications with the base station, usingthe one or more quick uplink channels, in accordance with the reducedTTI.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a base station (BS). The method generally includesreceiving, from a user equipment (UE), an indication that the UE iscapable of supporting low latency communications through one or morequick uplink channels, wherein the one or more quick uplink channelsenable a reduced transmission time interval (TTI) for the low latencycommunications having a shorter duration than a legacy TTI andperforming the low latency communications with the UE, using the one ormore quick uplink channels, in accordance with the reduced TTI.

According to certain aspects, the method further includes participatingin one or more procedures with the UE in accordance with the legacy TTI.In some cases, participating in the one or more procedures comprises atleast one of: transmitting synchronization signals to aid in cellsearch, transmitting system information blocks (SIBs), participating ina random access channel (RACH) procedure, transmitting a paging message,or participating in an idle mode procedure.

According to certain aspects, the method further includes transmitting,to the UE, parameters for performing the low latency communications, inresponse to receiving the indication. In some cases, the parametersindicate at least one of time or frequency resources for the one or morequick uplink channels. Additionally, in some cases the parametersindicate a mapping of downlink transmissions to resources for use inacknowledging the downlink transmissions using the one or more quickuplink channels.

According to certain aspects, a duration of the legacy TTI correspondsto a duration of a subframe, wherein the subframe includes two timeslots and the shorter duration of the reduced TTI corresponds to aduration of the time slots. In some cases, a first set of quick physicaluplink control channel (QPUCCH) formats, for transmitting uplink controlinformation, are supported in a first of the two time slots and a secondset of QPUCCH formats are supported in a second of the two time slots,wherein the second set is a reduced subset of the first set. In somecases, at least some of the QPUCCH formats of the first and second setsare based on legacy physical uplink control channel (PUCCH) formats.

According to certain aspects, the method further includes allocating theUE a first set of resource blocks (RBs) for transmitting a quickphysical uplink control channel (QPUCCH) in a first of the two timeslots and allocating the UE a second set of RBs, different from thefirst set of RBs, for transmitting a QPUCCH in a second of the two timeslots.

According to certain aspects, the UE is able to transmit a quickphysical uplink control channel (QPUCCH) in one, but not both, of thetwo time slots.

According to certain aspects, performing the low latency communicationscomprises receiving data, from the UE, in a first quick physical uplinkshared channel (QPUSCH) in one of the time slots.

According to certain aspects, the method further includes transmittingan indication of whether the data transmitted in the first QPUSCH wassuccessfully received in a quick physical downlink control channel(QPDCCH) transmitted from the base station in accordance with thereduced TTI. In some cases, the QPDCCH is transmitted during a time slota first number of subframes after the QPUSCH transmission in accordancewith the reduced TTI.

According to certain aspects, the method further includes schedulingQPUSCH transmissions from the UE and legacy physical uplink sharedchannel (PUSCH) transmissions from a legacy UE such that resources usedto acknowledge the QPUSCH and PUSCH transmissions do not collide.

According to certain aspects, the method further includes transmittingdata in a quick physical downlink shared channel (QPDSCH) to the UE inaccordance with the reduced TTI.

In some cases, performing low latency communications comprises receivingan indication of whether the QPDSCH transmission was successfullyreceived in a quick physical uplink control channel (QPUCCH).Additionally, in some cases, the QPUCCH is received in a time slot anumber of subframes after the QPDSCH transmission in accordance with thereduced TTI.

According to certain aspects, the method further includes schedulingQPDSCH transmissions to the UE and legacy physical downlink sharedchannel (PDSCH) transmissions to a legacy UE such that resources used toacknowledge the QPDSCH and PDSCH transmissions do not collide.

In some cases, performing the low latency communications comprisesreceiving at least one of a quick physical uplink shared channel(QPUSCH) or quick physical uplink control channel (QPUCCH) in one of thetwo time slots multiplexed with sounding reference signals (SRS).

Additionally, in some cases, performing the low latency communicationcomprises receiving a channel quality indicator (CQI) in a quickphysical uplink shared channel (QPUSCH) in one of the two time slots.

Certain aspects of the present disclosure provide an apparatus forwireless communication. The apparatus generally includes a memorycoupled with at least one processor, wherein the at least one processoris configured to: receive, from a user equipment (UE), an indicationthat the UE is capable of supporting low latency communications throughone or more quick uplink channels, wherein the one or more quick uplinkchannels enable a reduced transmission time interval (TTI) for the lowlatency communications having a shorter duration than a legacy TTI, andperform the low latency communications with the UE, using the one ormore quick uplink channels, in accordance with the reduced TTI.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forreceiving, from a user equipment (UE), an indication that the UE iscapable of supporting low latency communications through one or morequick uplink channels, wherein the one or more quick uplink channelsenable a reduced transmission time interval (TTI) for the low latencycommunications having a shorter duration than a legacy TTI and means forperforming the low latency communications with the UE, using the one ormore quick uplink channels, in accordance with the reduced TTI.

Certain aspects of the present disclosure provide a non-transitorycomputer-readable medium for wireless communications, comprising codefor receiving, from a user equipment (UE), an indication that the UE iscapable of supporting low latency communications through one or morequick uplink channels, wherein the one or more quick uplink channelsenable a reduced transmission time interval (TTI) for the low latencycommunications having a shorter duration than a legacy TTI andperforming the low latency communications with the UE, using the one ormore quick uplink channels, in accordance with the reduced TTI.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram conceptually illustrating an example of atelecommunications system, in accordance with an aspect of the presentdisclosure;

FIG. 2 is a diagram illustrating an example of an access network, inaccordance with an aspect of the present disclosure.

FIG. 3 is a diagram illustrating an example of a DL frame structure inLTE, in accordance with an aspect of the present disclosure.

FIG. 4 is a diagram illustrating an example of an UL frame structure inLTE, in accordance with an aspect of the present disclosure.

FIG. 5 is a diagram illustrating an example of a radio protocolarchitecture for the user and control planes, in accordance with anaspect of the present disclosure.

FIG. 6 is a diagram illustrating an example of an evolved Node B anduser equipment in an access network, in accordance with an aspect of thepresent disclosure.

FIG. 7 illustrates a flow diagram of example operations for managingexpedited user equipment (UE) communications at a UE, in accordance withcertain aspects of the present disclosure.

FIG. 8 illustrates a flow diagram of example operations for configuringand transmitting a downlink subframe to manage expedited communications,in accordance with certain aspects of the present disclosure.

FIG. 9 illustrates an example of a downlink frame structure for managingexpedited UE communications in a wireless communication system, inaccordance with aspects of the present disclosure.

FIG. 10 illustrates an example of a downlink frame structure formanaging machine type communications (MTC), in accordance with aspectsof the present disclosure.

FIG. 11 illustrates an example of a downlink frame structure formanaging Low Latency (LL) communications, in accordance with aspects ofthe present disclosure.

FIG. 12 illustrates example operations for wireless communications by auser equipment (UE), in accordance with aspects of the presentdisclosure.

FIG. 13 illustrates example operations for wireless communications by abase station (BS), in accordance with aspects of the present disclosure.

FIG. 14 is a diagram illustrating an example low latency uplink channeldesign, in accordance with aspects of the present disclosure.

FIG. 15 is a diagram illustrating example uplink Hybrid Automatic RepeatRequest (HARQ) transmissions, in accordance with aspects of the presentdisclosure.

FIG. 16 is a diagram illustrating example downlink Hybrid AutomaticRepeat Request (HARQ) transmissions, in accordance with aspects of thepresent disclosure.

DETAILED DESCRIPTION

Certain aspects of the present disclosure relate to an enhanced downlinkcontrol channel that may be used for managing machine typecommunications (MTC) and/or low latency (LL) communications. For LL,such a design may help reduce over-the-air latency by, for example, afactor of two while maintaining backward compatibility and co-existencewith legacy devices.

Additionally, certain aspects of the present disclosure may help enablelow latency communications between a user equipment (UE) and a basestation (BS) using quick uplink channels that enable a reducedtransmission time interval (TTI).

The techniques presented herein may help reduce latency as compared tolegacy uplink transmission, using quick uplink data and controlchannels. For purposes of the present disclosure, any channel that mayhave a transmission time interval (TTI) of a single slot (or a portionof a single slot) may be referred to as a Quick channel. These Quickchannels may include, in a non-limiting aspect, a Quick Physical UplinkControl Channel (QPUCCH), a Quick Enhanced Physical Uplink ControlChannel (QEPUCCH), and a Quick Physical Uplink Shared Channel (QPUSCH).Furthermore, a Quick channel as described in the present disclosure mayhave one or more channels or resource element blocks that are or can beallocated, assigned, or divided on a per-slot basis and/or have a TTI of0.5 ms.

Moreover, certain aspects of the present disclosure additionallyimplement frame scheduling of legacy channels (e.g., PDCCH, EPDCCH,PDSCH) alongside the Quick channel (e.g., QPUCCH, QEPUCCH, QPUSCH). Themethods and apparatus described herein may be implemented forapplications that are configured to utilize Quick channel schedulingand/or legacy scheduling. As the Quick LTE scheduling methods describedherein may utilize a 0.5 ms TTI rather than the 1 ms TTI of legacy,these methods may increase communication rates and may cut a round-triptime (RTT) associated with legacy LTE hybrid automatic repeat request(HARQ) procedures in half (e.g., from 8 ms to 4 ms or less).

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise.

Accordingly, in one or more aspects, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can compriseRAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic diskstorage or other magnetic storage devices, or any other medium that canbe used to carry or store desired program code in the form ofinstructions or data structures and that can be accessed by a computer.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), and floppy disk where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Referring first to FIG. 1, a diagram illustrates an example of awireless communications system 100, in which aspects of the presentdisclosure may be performed, for example, to manage communications inthe wireless communication system using enhanced downlink controlchannel to reduce transmission time interval (TTI) for low latencycommunications using quick uplink channels.

The wireless communications system 100 includes a plurality of accesspoints (e.g., base stations, eNBs, or WLAN access points) 105, a numberof user equipment (UEs) 115, and a core network 130. Access points 105may include an uplink scheduling component 602 configured to expeditecommunication of control information and user data with the number ofUEs 115 using a Quick LTE channel which may include a TTI of one slotfor some RE blocks. Similarly, one or more of UEs 115 may include anuplink transmitter component 661 configured to transmit and operateusing Quick LTE channel structure. Some of the access points 105 maycommunicate with the UEs 115 under the control of a base stationcontroller (not shown), which may be part of the core network 130 or thecertain access points 105 (e.g., base stations or eNBs) in variousexamples. Access points 105 may communicate control information and/oruser data with the core network 130 through backhaul links 132. Inexamples, the access points 105 may communicate, either directly orindirectly, with each other over backhaul links 134, which may be wiredor wireless communication links. The wireless communications system 100may support operation on multiple carriers (waveform signals ofdifferent frequencies). Multi-carrier transmitters can transmitmodulated signals simultaneously on the multiple carriers. For example,each communication link 125 may be a multi-carrier signal modulatedaccording to the various radio technologies described above. Eachmodulated signal may be sent on a different carrier and may carrycontrol information (e.g., reference signals, control channels, etc.),overhead information, data, etc.

In some examples, at least a portion of the wireless communicationssystem 100 may be configured to operate on multiple hierarchical layersin which one or more of the UEs 115 and one or more of the access points105 may be configured to support transmissions on a hierarchical layerthat has a reduced latency with respect to another hierarchical layer.In some examples a hybrid UE 115-a may communicate with access point105-a on both a first hierarchical layer that supports first layertransmissions with a first subframe type and a second hierarchical layerthat supports second layer transmissions with a second subframe type.For example, access point 105-a may transmit subframes of the secondsubframe type that are time division duplexed with subframes of thefirst subframe type.

In some examples, an access point 105-a may acknowledge receipt of atransmission by providing ACK/NACK for the transmission through, forexample, a HARQ scheme. Acknowledgments from the access point 105-a fortransmissions in the first hierarchical layer may be provided, in someexamples, after a predefined number of subframes following the subframein which the transmission was received. The time required to transmit anACK/NACK and receive a retransmission may be referred to as round triptime (RTT), and thus subframes of the second subframe type may have asecond RTT that is shorter than a RTT for subframes of the firstsubframe type.

In other examples, a second layer UE 115-b may communicate with accesspoint 105-b on the second hierarchical layer only. Thus, hybrid UE 115-aand second layer UE 115-b may belong to a second class of UEs 115 thatmay communicate on the second hierarchical layer, while legacy UEs 115may belong to a first class of UEs 115 that may communicate on the firsthierarchical layer only. Thus, second layer UE 115-b may operate withreduced latency compared to UEs 115 that operate on the firsthierarchical layer.

The access points 105 may wirelessly communicate with the UEs 115 viaone or more access point antennas. Each of the access points 105 sitesmay provide communication coverage for a respective coverage area 110.In some examples, access points 105 may be referred to as a basetransceiver station, a radio base station, a radio transceiver, a basicservice set (BSS), an extended service set (ESS), a NodeB, eNodeB, HomeNodeB, a Home eNodeB, or some other suitable terminology. The coveragearea 110 for a base station may be divided into sectors making up only aportion of the coverage area (not shown). The wireless communicationssystem 100 may include access points 105 of different types (e.g.,macro, micro, and/or pico base stations). The access points 105 may alsoutilize different radio technologies, such as cellular and/or WLAN radioaccess technologies. The access points 105 may be associated with thesame or different access networks or operator deployments. The coverageareas of different access points 105, including the coverage areas ofthe same or different types of access points 105, utilizing the same ordifferent radio technologies, and/or belonging to the same or differentaccess networks, may overlap.

In LTE/LTE-A network communication systems, the terms evolved Node B(eNodeB or eNB) may be generally used to describe the access points 105.The wireless communications system 100 may be a HeterogeneousLTE/LTE-A/ULL LTE network in which different types of access pointsprovide coverage for various geographical regions. For example, eachaccess point 105 may provide communication coverage for a macro cell, apico cell, a femto cell, and/or other types of cell. Small cells such aspico cells, femto cells, and/or other types of cells may include lowpower nodes or LPNs. A macro cell generally covers a relatively largegeographic area (e.g., several kilometers in radius) and may allowunrestricted access by UEs 115 with service subscriptions with thenetwork provider. A small cell would generally cover a relativelysmaller geographic area and may allow unrestricted access by UEs 115with service subscriptions with the network provider, for example, andin addition to unrestricted access, may also provide restricted accessby UEs 115 having an association with the small cell (e.g., UEs in aclosed subscriber group (CSG), UEs for users in the home, and the like).An eNB for a macro cell may be referred to as a macro eNB. An eNB for asmall cell may be referred to as a small cell eNB. An eNB may supportone or multiple (e.g., two, three, four, and the like) cells.

The core network 130 may communicate with the eNBs or other accesspoints 105 via a backhaul 132 (e.g., S1 interface, etc.). The accesspoints 105 may also communicate with one another, e.g., directly orindirectly via backhaul links 134 (e.g., X2 interface, etc.) and/or viabackhaul links 132 (e.g., through core network 130). The wirelesscommunications system 100 may support synchronous or asynchronousoperation. For synchronous operation, the access points 105 may havesimilar frame timing, and transmissions from different access points 105may be approximately aligned in time. For asynchronous operation, theaccess points 105 may have different frame timing, and transmissionsfrom different access points 105 may not be aligned in time.Furthermore, transmissions in the first hierarchical layer and secondhierarchical layer may or may not be synchronized among access points105. The techniques described herein may be used for either synchronousor asynchronous operations.

The UEs 115 are dispersed throughout the wireless communications system100, and each UE 115 may be stationary or mobile. A UE 115 may also bereferred to by those skilled in the art as a mobile station, asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal, a mobile terminal, a wireless terminal, a remoteterminal, a handset, a user agent, a mobile client, a client, or someother suitable terminology. A UE 115 may be a cellular phone, a personaldigital assistant (PDA), a wireless modem, a wireless communicationdevice, a handheld device, a tablet computer, a laptop computer, acordless phone, a wearable item such as a watch or glasses, a wirelesslocal loop (WLL) station, or the like. A UE 115 may be able tocommunicate with macro eNodeBs, small cell eNodeBs, relays, and thelike. A UE 115 may also be able to communicate over different accessnetworks, such as cellular or other WWAN access networks, or WLAN accessnetworks.

The communication links 125 shown in wireless communications system 100may include uplink (UL) transmissions from a UE 115 to an access point105, and/or downlink (DL) transmissions, from an access point 105 to aUE 115. The downlink transmissions may also be called forward linktransmissions while the uplink transmissions may also be called reverselink transmissions. The communication links 125 may carry transmissionsof each hierarchical layer which, in some examples, may be multiplexedin the communication links 125. The UEs 115 may be configured tocollaboratively communicate with multiple access points 105 through, forexample, Multiple Input Multiple Output (MIMO), carrier aggregation(CA), Coordinated Multi-Point (CoMP), or other schemes. MIMO techniquesuse multiple antennas on the access points 105 and/or multiple antennason the UEs 115 to transmit multiple data streams. Carrier aggregationmay utilize two or more component carriers on a same or differentserving cell for data transmission. CoMP may include techniques forcoordination of transmission and reception by a number of access points105 to improve overall transmission quality for UEs 115 as well asincreasing network and spectrum utilization.

As mentioned, in some examples access points 105 and UEs 115 may utilizecarrier aggregation (CA) to transmit on multiple carriers. In someexamples, access points 105 and UEs 115 may concurrently transmit in afirst hierarchical layer, within a frame, one or more subframes eachhaving a first subframe type using two or more separate carriers. Eachcarrier may have a bandwidth of, for example, 20 MHz, although otherbandwidths may be utilized. Hybrid UE 115-a, and/or second layer UE115-b may, in certain examples, receive and/or transmit one or moresubframes in a second hierarchical layer utilizing a single carrier thathas a bandwidth greater than a bandwidth of one or more of the separatecarriers. For example, if four separate 20 MHz carriers are used in acarrier aggregation scheme in the first hierarchical layer, a single 80MHz carrier may be used in the second hierarchical layer. The 80 MHzcarrier may occupy a portion of the radio frequency spectrum that atleast partially overlaps the radio frequency spectrum used by one ormore of the four 20 MHz carriers. In some examples, scalable bandwidthfor the second hierarchical layer type may be combined with othertechniques to provide shorter RTTs such as described above, to providefurther enhanced data rates.

Each of the different operating modes that may be employed by wirelesscommunication system 100 may operate according to frequency divisionduplexing (FDD) or time division duplexing (TDD). In some examples,different hierarchical layers may operate according to different TDD orFDD modes. For example, a first hierarchical layer may operate accordingto FDD while a second hierarchical layer may operate according to TDD.In some examples, OFDMA communications signals may be used in thecommunication links 125 for LTE downlink transmissions for eachhierarchical layer, while single carrier frequency division multipleaccess (SC-FDMA) communications signals may be used in the communicationlinks 125 for LTE uplink transmissions in each hierarchical layer.Additional details regarding implementation of hierarchical layers in asystem such as the wireless communications system 100, as well as otherfeatures and functions related to communications in such systems, areprovided below with reference to the following figures.

FIG. 2 is a diagram illustrating an example of an access network 200 inan LTE network architecture, in which aspects of the present disclosuremay be performed, for example, to manage communications in the wirelesscommunication system using enhanced downlink control channel to reducetransmission time interval (TTI) for low latency communications usingquick uplink channels.

In this example, the access network 200 is divided into a number ofcellular regions (cells) 202. One or more lower power class eNBs 208 mayhave cellular regions 210 that overlap with one or more of the cells202. The lower power class eNB 208 may be a femto cell (e.g., home eNB(HeNB)), pico cell, micro cell, or remote radio head (RRH). The macroeNBs 204 are each assigned to a respective cell 202 and are configuredto provide an access point to the core network 130 for all the UEs 206in the cells 202. In an aspect, eNBs 204 may include an uplinkscheduling component 602 configured to expedite communication of controlinformation and user data with the number of UEs 115 using an Quick LTEdata structure, for example but not limited to the data structureprovided in the downlink subframe structure 900 of FIG. 9, which mayinclude a TTI of one slot for some RE blocks. Similarly, one or more ofUEs 206 may include an uplink transmitter component 661 configured totransmit, decode and operate using the data structure. There is nocentralized controller in this example of an access network 200, but acentralized controller may be used in alternative configurations. TheeNBs 204 are responsible for all radio related functions including radiobearer control, admission control, mobility control, scheduling,security, and connectivity to the serving gateway 116.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the DL and SC-FDMAis used on the UL to support both frequency division duplexing (FDD) andtime division duplexing (TDD). As those skilled in the art will readilyappreciate from the detailed description to follow, the various conceptspresented herein are well suited for LTE applications. However, theseconcepts may be readily extended to other telecommunication standardsemploying other modulation and multiple access techniques. By way ofexample, these concepts may be extended to Evolution-Data Optimized(EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interfacestandards promulgated by the 3rd Generation Partnership Project 2(3GPP2) as part of the CDMA2000 family of standards and employs CDMA toprovide broadband Internet access to mobile stations. These concepts mayalso be extended to Universal Terrestrial Radio Access (UTRA) employingWideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA;Global System for Mobile Communications (GSM) employing TDMA; andEvolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSMare described in documents from the 3GPP organization. CDMA2000 and UMBare described in documents from the 3GPP2 organization. The actualwireless communication standard and the multiple access technologyemployed will depend on the specific application and the overall designconstraints imposed on the system.

The eNBs 204 may have multiple antennas supporting MIMO technology. Theuse of MIMO technology enables the eNBs 204 to exploit the spatialdomain to support spatial multiplexing, beamforming, and transmitdiversity. Spatial multiplexing may be used to transmit differentstreams of data simultaneously on the same frequency. The data steamsmay be transmitted to a single UE 206 to increase the data rate or tomultiple UEs 206 to increase the overall system capacity. This isachieved by spatially precoding each data stream (i.e., applying ascaling of an amplitude and a phase) and then transmitting eachspatially precoded stream through multiple transmit antennas on the DL.The spatially precoded data streams arrive at the UE(s) 206 withdifferent spatial signatures, which enables each of the UE(s) 206 torecover the one or more data streams destined for that UE 206. On theUL, each UE 206 transmits a spatially precoded data stream, whichenables the eNB 204 to identify the source of each spatially precodeddata stream.

Spatial multiplexing is generally used when channel conditions are good.When channel conditions are less favorable, beamforming may be used tofocus the transmission energy in one or more directions. This may beachieved by spatially precoding the data for transmission throughmultiple antennas. To achieve good coverage at the edges of the cell, asingle stream beamforming transmission may be used in combination withtransmit diversity.

In the detailed description that follows, various aspects of an accessnetwork will be described with reference to a MIMO system supportingOFDM. OFDM is a spread-spectrum technique that modulates data over anumber of subcarriers within an OFDM symbol. The subcarriers are spacedapart at precise frequencies. The spacing provides “orthogonality” thatenables a receiver to recover the data from the subcarriers. In the timedomain, a guard interval (e.g., cyclic prefix) may be added to each OFDMsymbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMAin the form of a DFT-spread OFDM signal to compensate for highpeak-to-average power ratio (PAPR).

FIG. 3 is a diagram 300 illustrating an example of a DL frame structurein LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames.Each sub-frame may include two consecutive time slots. A resource gridmay be used to represent two time slots, each time slot including aresource element block. The resource grid is divided into multipleresource elements. In LTE, a resource element block may contain 12consecutive subcarriers in the frequency domain and, for a normal cyclicprefix in each OFDM symbol, 7 consecutive OFDM symbols in the timedomain, or 84 resource elements. For an extended cyclic prefix, aresource element block may contain 6 consecutive OFDM symbols in thetime domain and has 72 resource elements. Some of the resource elements,as indicated as R 302, 304, include DL reference signals (DL-RS). TheDL-RS include Cell-specific RS (CRS) (also sometimes called common RS)302 and UE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only onthe resource element blocks upon which the corresponding PDSCH ismapped. The number of bits carried by each resource element depends onthe modulation scheme. Thus, the more resource element blocks that a UEreceives and the higher the modulation scheme, the higher the data ratefor the UE.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structurein LTE. The available resource element blocks for the UL may bepartitioned into a data section and a control section. The controlsection may be formed at the two edges of the system bandwidth and mayhave a configurable size. The resource element blocks in the controlsection may be assigned to UEs for transmission of control information.The data section may include all resource element blocks not included inthe control section. The UL frame structure results in the data sectionincluding contiguous subcarriers, which may allow a single UE to beassigned all of the contiguous subcarriers in the data section.

A UE may be assigned resource element blocks 410 a, 410 b in the controlsection to transmit control information to an eNB. The UE may also beassigned resource element blocks 420 a, 420 b in the data section totransmit data to the eNB. The UE may transmit control information in aphysical UL control channel (PUCCH) on the assigned resource elementblocks in the control section. The UE may transmit only data or bothdata and control information in a physical UL shared channel (PUSCH) onthe assigned resource element blocks in the data section. A ULtransmission may span both slots of a subframe and may hop acrossfrequency.

A set of resource element blocks may be used to perform initial systemaccess and achieve UL synchronization in a physical random accesschannel (PRACH) 430. The PRACH 430 carries a random sequence and cannotcarry any UL data/signaling. Each random access preamble occupies abandwidth corresponding to six consecutive resource element blocks. Thestarting frequency is specified by the network. That is, thetransmission of the random access preamble is restricted to certain timeand frequency resources. There is no frequency hopping for the PRACH.The PRACH attempt is carried in a single subframe (1 ms) or in asequence of few contiguous subframes and a UE can make only a singlePRACH attempt per frame (10 ms).

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for the UE and the eNB is shown with three layers: Layer 1,Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer andimplements various physical layer signal processing functions. The L1layer will be referred to herein as the physical layer 506. Layer 2 (L2layer) 508 is above the physical layer 506 and is responsible for thelink between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource element blocks) in one cellamong the UEs. The MAC sublayer 510 is also responsible for HARQoperations.

In the control plane, the radio protocol architecture for the UE and eNBis substantially the same for the physical layer 506 and the L2 layer508 with the exception that there is no header compression function forthe control plane. The control plane also includes a radio resourcecontrol (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516is responsible for obtaining radio resources (i.e., radio bearers) andfor configuring the lower layers using RRC signaling between the eNB andthe UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650in an access network. In the DL, upper layer packets from the corenetwork are provided to a controller/processor 675. Thecontroller/processor 675 implements the functionality of the L2 layer.In the DL, the controller/processor 675 provides header compression,ciphering, packet segmentation and reordering, multiplexing betweenlogical and transport channels, and radio resource allocations to the UE650 based on various priority metrics. The controller/processor 675 isalso responsible for HARQ operations, retransmission of lost packets,and signaling to the UE 650.

The transmit (TX) processor 616 implements various signal processingfunctions for the L1 layer (i.e., physical layer). The signal processingfunctions includes coding and interleaving to facilitate forward errorcorrection (FEC) at the UE 650 and mapping to signal constellationsbased on various modulation schemes (e.g., binary phase-shift keying(BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying(M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded andmodulated symbols are then split into parallel streams. Each stream isthen mapped to an OFDM subcarrier, multiplexed with a reference signal(e.g., pilot) in the time and/or frequency domain, and then combinedtogether using an Inverse Fast Fourier Transform (IFFT) to produce aphysical channel carrying a time domain OFDM symbol stream. The OFDMstream is spatially precoded to produce multiple spatial streams.Channel estimates from a channel estimator 674 may be used to determinethe coding and modulation scheme, as well as for spatial processing. Thechannel estimate may be derived from a reference signal and/or channelcondition feedback transmitted by the UE 650. Each spatial stream isthen provided to a different antenna 620 via a separate transmitter618TX. Each transmitter 618TX modulates an RF carrier with a respectivespatial stream for transmission. In addition, eNB 610 may include anuplink scheduling component 602 configured to expedite communication ofcontrol information and user data with the number of UEs 115 accordingto certain aspects of the present disclosure.

At the UE 650, each receiver 654RX receives a signal through itsrespective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 656. The RX processor 656 implements various signalprocessing functions of the L1 layer. The RX processor 656 performsspatial processing on the information to recover any spatial streamsdestined for the UE 650. If multiple spatial streams are destined forthe UE 650, they may be combined by the RX processor 656 into a singleOFDM symbol stream. The RX processor 656 then converts the OFDM symbolstream from the time-domain to the frequency domain using a Fast FourierTransform (FFT). The frequency domain signal comprises a separate OFDMsymbol stream for each subcarrier of the OFDM signal. The symbols oneach subcarrier, and the reference signal, is recovered and demodulatedby determining the most likely signal constellation points transmittedby the eNB 610. These soft decisions may be based on channel estimatescomputed by the channel estimator 658. The soft decisions are thendecoded and deinterleaved to recover the data and control signals thatwere originally transmitted by the eNB 610 on the physical channel. Thedata and control signals are then provided to the controller/processor659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the UL, the controller/processor 659provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations. In addition, UE 650 may include an uplinktransmitter component 661 configured to receive, decode and operateusing the data structure of the present disclosure.

In the UL, a data source 667 is used to provide upper layer packets tothe controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the DL transmission by the eNB 610, thecontroller/processor 659 implements the L2 layer for the user plane andthe control plane by providing header compression, ciphering, packetsegmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the eNB 610.The controller/processor 659 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the eNB 610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the eNB 610 may be used by the TXprocessor 668 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 668 are provided to different antenna 652 via separatetransmitters 654TX. Each transmitter 654TX modulates an RF carrier witha respective spatial stream for transmission.

The UL transmission is processed at the eNB 610 in a manner similar tothat described in connection with the receiver function at the UE 650.Each receiver 618RX receives a signal through its respective antenna620. Each receiver 618RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 670. The RXprocessor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the UL, the controller/processor 675provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

EXAMPLE ENHANCED DOWNLINK CONTROL CHANNEL DESIGN

Certain aspects of the present disclosure relate to an enhanced downlinkcontrol channel that may be used for managing machine typecommunications (MTC) and/or low latency (LL) communications. For LL,such a design may help reduce over-the-air latency by, for example, afactor of two while maintaining backward compatibility and co-existencewith legacy devices.

A user equipment (UE) may comprise, be implemented as, or be known as anaccess terminal (AT), a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a remote device, awireless device, a device, a user terminal, a user agent, a user device,a user station, machine type communications (MTC) device or some otherterminology. Examples of UEs include cellular phones (e.g., smartphones), tablets, laptops, netbooks, smartbooks, ultrabooks, navigationdevices, camera devices, gaming devices, etc. Examples of MTC devicesinclude various wireless sensors, monitors, detectors, meters, or othertype data monitoring, generating, or relaying devices that may beexpected to operate (possibly unattended) for years on a single batterycharge.

FIG. 7 illustrates example operations 700 for wireless communications,in accordance with aspects of the present disclosure. The operations 700may be performed, for example, by a user equipment, e.g., the userequipment 115 from FIG. 1, the user equipment 206 from FIG. 2, and/orthe user equipment 650 from FIG. 6.

The operations 700 begin at 702 by receiving, at a UE, in a downlinksubframe comprising two slots, at least one type of advanced physicaldownlink control channel (aPDCCH) from a base station (BS). According tocertain aspects, the aPDCCH may include newer types of physical downlinkcontrol channel mechanisms, e.g., quick physical downlink controlchannel (QPDCCH), quick enhanced physical downlink control channel(QEPDCCH), etc. At 704, the user equipment demodulates the aPDCCH basedon a cell-specific reference signals (CRS).

FIG. 8 illustrates example operations 800 for wireless communications,in accordance with aspects of the present disclosure. The operations 800may be performed, for example, by a base station, e.g., the access point105 from FIG. 1, the eNB 204 from FIG. 2, and/or the eNB 610 from FIG.6.

The operation 800 begin at 802 by transmitting, in a downlink subframecomprising two slots, at least one type of advanced physical downlinkcontrol channel (aPDCCH) to a user equipment. At 804, the base stationmay transmit cell-specific reference signals (CRS) in the downlinksubframe for the UE to use for demodulating the aPDCCH.

One focus of the traditional Long Term Evolution (LTE) design is on theimprovement of spectral efficiency, ubiquitous coverage, enhancedQuality of Service (QoS) support, and so on. This focus typicallyresults in high-end devices, such as the state-of-art smart-phones,tablets, etc. However, low cost low rate devices may also need to besupported. For example, some market projections show that the number oflow cost devices may largely exceed today's cell phones. Certainfeatures have been explored in wireless systems, for example, reductionof maximum bandwidth, single receive radio frequency (RF) chain,reduction of peak rate, reduction of transmit power, half duplexoperation, etc.

In many applications, coverage enhancement for MTC devices may bedesirable. In addition to low cost requirement, 15-20 dB coverageenhancement may be needed to cover devices in a low coverage scenario(e.g., in a basement). In order to meet these requirements, large TTIbundling is proposed to achieve 15-20 dB link budget gain. On the DL,TTI bundling has been proposed for Physical Broadcast Channel (PBCH),PDCCH/EPDCCH, Physical Hybrid-ARQ Indicator Channel (PHICH), andPhysical Downlink Shared Channel (PDSCH). On the UL, TTI bundling hasbeen proposed for Random Access Channel (RACH), Physical Uplink ControlChannel (PUCCH), and Physical Uplink Shared Channel (PUSCH).

For MTC, narrowband operation is considered for the LTE Rel. 13 whereonly six resource blocks (RBs) are used in RF and baseband processing.With this requirement, the current PDCCH design may not be used, as itspans the entire band. EPDCCH can be used, but it becomes veryinefficient. For low latency LTE design, one slot based QEPDCCH isconsidered. Similarly, the current Demodulation Reference Signal (DMRS)based design is not efficient.

For complexity reduction, narrowband operation of six RBs is proposedfor MTC communications. There are two control channel structuresconsidered for MTC, however, there are issues with both of theapproaches. In a first approach, PDCCH-like control channel may beemployed with Time Division Multiplexing (TDM) control in time domain,and Cell-specific Reference Signal (CRS) based demodulation. Since thePDCCH spans the entire bandwidth, new design needs to be considered forMTC. In a second approach, EPDCCH-like control channel may be utilizedwith Frequency Division Multiplexing (FDM) control, and DMRS baseddemodulation. However, since both DMRS and CRS are present, the overheadmay be significant.

In accordance with aspects of the present disclosure, the low latency(LL) PHY design objective may be to reduce over-the-air LTE latency by afactor of two, e.g., from 8 ms RTT to 4 ms RTT with minimalspecification and implementation impact. In addition, backwardcompatibility and co-existence with legacy LTE devices (i.e., non-MTCdevices) may be maintained.

In accordance with aspects of the present disclosure, a key technicalsolution may be based on enhanced data communications with 0.5 ms TTI,wherein the LL channel may be based on EPDCCH/PDSCH/PUCCH/PUSCH slotstructure. Similarly, there are two options for the control channelstructure.

In an aspect, LL DL control channel design may be based on a PDCCH-basedQuick DL Control Channel (QPDCCH). The legacy control region may be usedin slot 0 for scheduling data. The QPDCCH may reuse a PDCCH ControlChannel Element (CCE) structure and be fully multiplexed with otherlegacy control channels. New downlink control information (DCI) may beneeded to indicate slot based versus subframe based assignment. Thisapproach may allow HARQ RTT of, for example, 4 ms with slot based datacommunications. In the DL, QPDCCH may schedule slot 0 QPDSCH in asubframe n, and in the UL, QPDCCH may schedule slot 0 QPUSCH in asubframe n+2.

In another aspect, a LL DL control channel design may be based on anEPDCCH-based Quick DL Control Channel (QEPDCCH). In this case, thecurrent EPDCCH may be simply split into two slots. The same EnhancedControl Channel Element (ECCE) resources may be present in each slot asthe current EPDCCH. Simpler multiplexing with legacy EPDCCH may beachieved as well as across different LL users. The aggregation level maybe increased by approximately two times to maintain similar coverage,which may be similar to the current EPDCCH design for special subframeswith short duration. This approach may support both distributed andlocalized formats, and both DL and UL grants.

FIG. 9 is illustrates an example of a downlink subframe structure 900for managing expedited UE communications in a wireless communicationsystem, in accordance with aspects of the present disclosure. In anaspect of the present disclosure, the downlink subframe structure 900may comprise a slot-based downlink channel PDCCH. In an aspect, theslot-based PDCCH may be divided in the time domain (horizontally) intotwo slots (e.g., slot 0 and slot 1). Furthermore, the temporal duration(horizontal axis) of some resource element blocks of the slot-basedPDCCH may be one slot (0.5 ms TTI). As such, by incorporating controland data channel resource element blocks having a TTI of one slot (0.5ms), the downlink channel as illustrated in FIG. 9 allows for lowerlatency for downlink transmissions relative to, for example, resourceelement blocks of legacy LTE, which may have a downlink resource elementblock TTI of one subframe (1 ms).

As illustrated in FIG. 9, the slot-based downlink channel may comprise alegacy control region 902 for scheduling legacy devices that includesevery resource element of symbol 0. The slot-based downlink channelillustrated in FIG. 9 may further comprise an ePDCCH 904 spanning eachof the slots 0 and 1 (e.g., from symbols 1 to 13). Moreover, theslot-based downlink channel from FIG. 9 may comprise QEPDCCH1 906 basedon DMRS in slot 0 (e.g., from symbols 1 to 6), and QEPDCCH3/QEPDCCH4 908with an uplink resource grant for a UE receiving the subframe 900. Asshown, QEPDCCH3/QEPDCCH4 908 may span symbols 7 to 13 of slot 1.

As illustrated in FIG. 9, the slot-based downlink channel may comprisethe downlink data channel grant QPDSCH1 910 assigned by QEPDCCH1 906 inslot 0 (e.g., from symbols 1 to 6), and the downlink data channel grantQPDSCH 912 assigned by QEPDCCH3 908 in slot 1 (e.g., from symbols 7 to13). In addition, as illustrated in FIG. 9, the slot-based downlinkchannel may comprise one or more legacy downlink channels (e.g., regularPDSCH 914) having a two-slot TTI assigned by a control region (e.g.,assigned by PDCCH or EPDCCH).

In some cases, there may be certain issues to address for LL devices.For example, for the slot based QEPDCCH design, the DMRS in a slot maynot be sufficient for demodulation. However, increasing the DMRS densitymay lead to a large overhead as the available resources are alreadyreduced by half

Additionally, there are also certain issues for MTC devices to beresolved. For example, an MTC device may rely on CRS to decode physicalbroadcast control channel (PBCH), so CRS processing may need to besupported. For EPDCCH processing, relying on just DMRS may not besufficient especially for the coverage limited users.

Certain aspects of the present disclosure present an enhanced DL controlchannel structure for both MTC and low latency (LL) with 0.5 ms TTI. Theenhanced control channel may have and FDM structure similar to EPDCCHand may use CRS, instead of DRMS, for demodulation. Thus, since CRS isused for demodulation, a UE can perform longer averaging to improvechannel estimation. Additionally, since DRMS is not used, more resourcescan be used to transmit data tones.

Aspects of the present disclosure present new control channel, referredto as a Machine type communication PDCCH (e.g., MPDCCH), for MTC. Thiscontrol channel may span the entire subframe except, for example, for alegacy control region. The starting symbol may be signaled throughSystem Information (SI), Radio Resource Control (RRC), dynamically, orfixed by a wireless communication standard. As discussed above, DMRS maynot be transmitted in this new DL control channel design. Thus, enhancedcontrol channel elements (ECCEs) may also occupy the resources that aredefined for EPDCCH DMRS, which may reduce overhead and improve codingfor data. In an aspect of the present disclosure, demodulation may relysolely on CRS. This may provide longer averaging for channel estimationenhancements, as noted above.

With this new control channel design, MTC may rely on CRS fordemodulation for PBCH and MPDCCH. For PDSCH, the support for only CRSbased demodulations may be further restricted. Thus, the MTC UE does notneed to perform any DMRS based demodulation, which provides complexitysavings.

FIG. 10 illustrates an example of an enhanced downlink subframestructure 1000 for managing machine type communications (MTC), inaccordance with aspects of the present disclosure. The downlink subframestructure 1000 may be divided in time domain into two slots (e.g., slot0 and slot 1), each slot lasting, for example, 0.5 ms. As illustrated inFIG. 10, the downlink subframe structure 1000 may comprise a legacycontrol region 1002 for scheduling that includes every resource elementof a symbol of slot 0, and it may further comprise ePDCCH 1004 spanningeach of the slots 0 and 1. In an aspect, ePDCCH/QPDCCH/QEPDCCH mayutilize both CRS and DMRS for demodulation.

As illustrated in FIG. 10, the downlink subframe structure 1000 maycomprise a Machine type communication Physical Downlink Control Channel(MPDCCH) with CRR for demodulation 1006, which may span both slots 0 and1. As illustrated in FIG. 10, the downlink subframe structure 1000 mayfurther comprise MTC data traffic 1008, which may also span both slots 0and 1. In addition, as illustrated in FIG. 10, the downlink subframestructure 1000 may comprise one or more legacy downlink channels (e.g.,regular PDSCH 1010) having a two-slot TTI assigned by a control region(e.g., assigned by PDCCH or EPDCCH).

Aspects of the present disclosure also present a new control channel forLL (e.g., QEPDCCH). According to certain aspects, for LL, the QEPDCCHmay span a single slot (as opposed to an entire subframe) except for thelegacy control region in slot 0.

FIG. 11 illustrates an example of a downlink subframe structure 1100 forLow Latency (LL) communications, in accordance with aspects of thepresent disclosure. For example, the downlink subframe structure 1100may be divided in time domain into two slots (e.g., slot 0 and slot 1),each slot lasting, for example, 0.5 ms. As illustrated in FIG. 11, thedownlink subframe structure 1100 may comprise a legacy control region1102 for scheduling legacy UEs and may include every resource element ofa symbol 0 of slot 0. Additionally, as illustrated, the DL subframestructure may further comprise an ePDCCH 1104 spanning each of the slots0 and 1.

As illustrated in FIG. 11 and in accordance with aspects of the presentdisclosure, the downlink subframe structure 1100 may comprise QEPDCCH11106 with CRS for demodulation in slot 0 and QEPDCCH3/QEPDCCH4 1108 withan uplink resource grant in slot 1 for a user equipment receiving thesubframe 1100. In an aspect, at least one of QEPDCCH1 1106, QEPDCCH31108, or QEPDCCH4 1108 may utilize both CRS and DMRS for demodulation.

As illustrated in FIG. 11, the downlink subframe structure 1100 mayfurther comprise the downlink data channel grant QPDSCH1 1110 assignedby QEPDCCH1 1106 in slot 0, and the downlink data channel grant QPDSCH1112 assigned by QEPDCCH3 1108 in slot 1. In addition, as illustrated inFIG. 11, the downlink subframe structure 1100 may comprise one or morelegacy downlink channels (e.g., regular PDSCH 1114) having a two-slotTTI assigned by a control region (e.g., assigned by PDCCH or EPDCCH).

According to certain aspects, the starting symbol for the QEPDCCH (e.g.,QEPDCCH1 1106) may be signaled dynamically, fixed by a wirelesscommunication standard, or by using System Information (SI) and/or RadioResource Control (RRC). As discussed above, CRS may be transmitted andused for demodulation instead of DRMS. Thus, ECCEs may also occupy theresources that are defined for EPDCCH DMRS. According to certainaspects, except for not transmitting DMRS, the design of the QEPDCCH mayfollow the same as EPDCCH, e.g., regarding ECCE, aggregation level, etc.In an aspect, demodulation may rely solely on CRS, which may providelonger averaging for channel estimation enhancements. Additionally, theLL device has more flexibility to improve channel estimation for thecritical low latency communications, which may only have impact on thedevice power consumption, as the latency for data communications atleast stays the same.

EXAMPLE LOW LATENCY UPLINK CHANNEL DESIGN

As noted above, aspects of the present disclosure may help enable lowlatency communications between a user equipment (UE) and a base station(BS) using quick uplink channels that enable a reduced transmission timeinterval (TTI).

For example, certain aspects of the present disclosure providetechniques that may help reduce over-the-air latency in LTE systems by afactor of 2 (e.g., from 8 ms round trip time (RTT) to 4 ms), whilemaintaining backward compatibility and co-existence with legacy LTEdevices (e.g., devices that do not support the low latencycommunications described herein).

According to certain aspects, low latency communications may be enabledby using reduced transmission time intervals (TTIs) relative to legacyTTIs (i.e., TTIs used for legacy devices). For example, in some cases, a0.5 ms TTI may be used for a low latency (LL) channel based on aphysical downlink control channel (PDCCH), enhanced PDCCH (ePDCCH),PDSCH, PUCCH, and/or PUSCH slot structure. That is, for a 0.5 ms TTI,the LL channel may be based on time slots rather than subframes(assuming an LTE subframe that includes 2 time slots of 0.5 ms each). Insome cases, low latency communications may be achieved using a differentapproach, for example, with a (conventional LTE) 1 ms TTI, but withtightened processing requirements and timing advance (TA) restriction toallow 2 ms HARQ turnaround time instead of 4 s.

In some cases, in order to support 0.5 ms TTI bundling within thecurrent LTE system with backward compatibility and integration withother users, a device capable of supporting reduced TTIs may be requiredto perform certain procedures (e.g., cell search, SIB reading, RACHprocedure, paging, and idle mode procedure) according to a legacy 1 mssubframe structure.

According to certain aspects, a UE operating according to LL datacommunications (e.g., operating using 0.5 ms subframe structure) mayindicate LL capability to a serving eNB during or after connectionsetup. In response, the eNB may provide configuration information (e.g.,LL parameters, such as channel locations, starting CCE, etc.) for DL/ULchannels. In some cases, the LL parameters may include time (e.g., timeinstances) and/or frequency resources for LL channels (e.g., quickphysical uplink control channel, QPUCCH, and quick physical uplinkshared channel, QPUSCH). Additionally, the LL parameters may alsoindicate a starting symbol for a DL data channel (e.g., quick enhancedphysical downlink shared channel, QEPDSCH) and a DL control channel(e.g., Quick Enhanced Physical Downlink Control Channel, QEPDCCH). TheLL parameters may also indicate new resources allocated for QPUCCHacknowledgement (ACK) which, as will be described in greater detailbelow, may be different than a regular (i.e., legacy) PUCCH ACK. Theparameters may also provide a new mapping rule for LL communications,indicating a mapping of resources that is different than the mappingused for legacy communications, for example, for indicating the use ofdifferent resources from the legacy mapping).

According to certain aspects, the LL parameters may be broadcast (e.g.,in a system information block, SIB), provided through a radio resourcecontrol (RRC) message(s), and/or signaled using dynamic signaling by aneNB.

FIG. 12 illustrates example operations 1200 for low latency wirelesscommunications, in accordance with aspects of the present disclosure.The operations 1200 may be performed, for example, by a user equipment(UE) capable of supporting reduced TTIs (e.g., as compared to legacyUEs). For example, operations 1200 may be performed by the userequipment 115 from FIG. 1, the user equipment 206 from FIG. 2, and/orthe user equipment 650 from FIG. 6.

Operations 1200 begin, at 1202, by providing, to a base station, anindication that the UE is capable of supporting low latencycommunications through one or more quick uplink channels, wherein theone or more quick uplink channels enable a reduced transmission timeinterval (TTI) for the low latency communications having a shorterduration than a legacy TTI. At 1204, the UE performs the low latencycommunications with the base station, using the one or more quick uplinkchannels, in accordance with the reduced TTI.

FIG. 13 illustrates example operations 1300 for low latency wirelesscommunications, in accordance with aspects of the present disclosure.The operations 1300 may be performed, for example, by a base stationcapable of supporting reduced TTIs. For example, the operations 1300 maybe performed by the access point 105 from FIG. 1, the eNB 204 from FIG.2, and/or the eNB 610 from FIG. 6.

The operations 1300 begin, at 1302, by receiving, from a user equipment(UE), an indication that the UE is capable of supporting low latencycommunications through one or more quick uplink channels, wherein theone or more quick uplink channels enable a reduced transmission timeinterval (TTI) for the low latency communications having a shorterduration than a legacy TTI. At 1304, the base station performs the lowlatency communications with the UE using the one or more quick uplinkchannels transmitted in accordance with the reduced TTI.

FIG. 14 illustrates an example uplink control channel design for anuplink subframe 1400 using a reduced TTI that may be used by a UE and/oran eNB to perform low latency communications (e.g., in accordance withthe operations 1200 and/or 1300 described above).

For example, as shown in FIG. 14, to support LL communications andbackward compatibility, control and data channel resource element blocksfor quick physical uplink control channels (QPUCCHs) and/or quickphysical uplink shared channels (QPUSCHs) may be placed into each slotof the uplink subframe 1400, thus reducing the TTI to one time slot(e.g., 0.5 ms), rather than to one subframe (e.g., 1 ms). For example,as illustrated in FIG. 14, Slot 0 comprises QPUSCH1 at 1402, QPUSCH2 at1404, and QPUCCH at 1406. Additionally, Slot 1 comprises QPUCCH at 1408and QPUSCH3 at 1410.

According to certain aspects, the 0.5 ms-TTI QPUCCH (e.g., at 1406and/or 1408) may be based on a legacy PUCCH format (e.g., one of formats2/2 a/2 b/1/1 a/1 b/3). In some cases, each slot of the uplink subframe1400 may use a different format. For example, Slot 0 may use a fulllength format, while Slot 1 may use a shortened format (e.g., due to anSRS region 1412). In some cases, since formats 2 a and 2 b rely on thedifference between pilots in two slots for signaling ACK bits, a slotbased PUCCH using format 2 a and 2 b may not be supported.

Additionally, QPUCCH may use the same frequency location as legacyPUCCH. QPUCCH in different slots may use different RBs and LL UE may useeither slot 0 or slot 1 (but in some cases, not both). In some cases,there may be no hopping from the perspective of a UE that supports LLcommunications. Group hopping and sequence hopping may also be supportedfor QPUCCH in the same way as legacy PUCCH, but may only use one slotinstead of two. According to certain aspects, if group/sequence hoppingis being used for LL communications, the LL UE may follow the samegroup/sequence determination as legacy UEs.

As described above, QPUCCH may be based on legacy PUCCHformats/structures. For example, for formats 1, 1 a, 1 b, and 2, theQPUCCH may use the same structure as the legacy PUCCH, but may only spana single slot duration. Additionally, for different formats, there mayexist different options for implementing the QPUCCH. For example, forformat 3, the QPUCCH may (1) be based on the same structure as thelegacy PUCCH, but may only span a single slot structure. Additionally,another way to support QPUCCH using format 3 may be to extend the one RBdesign to a two RB design with the same code rate and resource mapping.For example, Inverse Discrete Fourier Transform (IDFT) may be performedover 2 RB instead of 1 RB. Another option is to perform a differentcoding for PUCCH format 3 to take into account the fact that only halfof the coded bits are available in one slot.

In some cases, QPUCCH may not support certain existing legacy PUCCHformats. For example, format 2 a/2 b may not be supported. Instead a newmapping rule may be defined such that if information is to be sent usingformats 2 a or 2 b the information may be mapped and sent on format 3with a single slot duration. For example, the UE may send ACK with CQI,using format 3 instead of format 2 a/2 b.

Additionally, as illustrated in FIG. 14, QPUSCH for different UEs may bemultiplexed in each slot. For example, as illustrated, QPUSCH1 at 1402and QPUSCH2 at 1404 corresponding to two UEs may be multiplexed intoSlot 0, while QPUSCH3 at 1410 corresponding to a third user may bemultiplexed into Slot 1. In certain aspects, group and sequence hoppingmay be supported, as well as uplink control information (UCI) on PUSCH.

As illustrated in FIG. 15, according to certain aspects, the reducedTTIs (i.e., reduced to 0.5 ms) proposed herein may allow HARQ round triptimes (RTTs) to also be reduced. For example, reduced TTIs may allow forreduced UL HARQ RTTs.

In legacy LTE design, the physical hybrid indicator channel (PHICH)resource (carrying ACK/NACK) in subframe n is mapped to a PUSCHtransmission from subframe n-4 (4 ms prior to the subframe with PHICH).Moreover, the PUSCH (being ACK'd) is also mapped to a PDCCH 4 subframesprior to the PUSCH. For example, as illustrated in FIG. 15, the PHICHtransmitted in subframe SF n+5 is mapped to (and carries an ACK for) thePUSCH transmitted in subframe SF m+1 which, in turn, is mapped to thePDCCH transmitted in subframe SF n−3 (e.g., that provided the grant forthe PUSCH). Thus, as illustrated, the HARQ RTT for legacy communications1502 may be 8 ms (i.e., the time from when the PDCCH schedules the ULHARQ transmission to when that UL HARQ transmission is acknowledged).

According to certain aspects, however, using the QPDCCH and QPUSCHpresented herein, UL HARQ RTT may be reduced, for example, from 8 ms to4 ms. For example, as illustrated in FIG. 15, this reduced RTT 1504 mayresult from the QPUSCH transmission (transmitted in a first slot ofsubframe m−2) being ACK'd via a QPDCCH (transmitted in a first slot ofsubframe m). Further, as illustrated, the QPUSCH may be scheduled via aQPDCCH sent in a first slot of subframe m−4).

Similarly, as illustrated in FIG. 16, reduced TTIs may also allow forreduced DL HARQ RTTs. In legacy LTE design, a PDSCH transmission (sentin subframe n-3) is ACK'd via a PUCCH transmission in subframe m+1.Further, the retransmission of PDSCH occurs in subframe n+5, againresulting in a HARQ RTT of 8 ms.

According to certain aspects, however, using the QPDCCH and QPUSCHpresented herein, may reduce the DL HARQ RTT, for example, from 8 ms to4 ms. As illustrated in FIG. 16, this reduced RTT result from the QPDSCHtransmission (transmitted in a first slot of subframe n−4) being ACK'dvia a QPUCCH (transmitted in a first slot of subframe m−2). Further, asillustrated, the QPDSCH may be retransmitted in a first slot of subframen).

As discussed above, legacy PUCCH ACKs may be mapped to DL assignmentsthat occurred 4 ms prior to the PUCCH ACK. As a result, for LL HARQ RTTsof 2 ms, it may be possible that QPUCCH ACK resources (mapped to 2 msbefore the QPUCCH ACK) may collide with some legacy UEs PUCCH ACKresources. Thus, certain aspects of the present disclosure providesolutions for avoiding a possible collision between QPUCCH and PUCCHresources.

For example, one option to prevent collision between QPUCCH and PUCCHresources may be to design a new mapping rule for LL ACK having 2 msturnaround (not shown in Figure). Another option to prevent collisionbetween QPUCCH and PUCCH collision may be for an eNB to scheduledownlink data transmissions for legacy UEs and LL UEs in a mannerdesigned to avoid collisions. In both options, slot-based PUCCHtransmissions may be mapped to slot-based DL assignments. From the LLUE's perspective, using same frequency resources across slots may appearas if no hopping is being used. In some cases, the QPUCCH may use thesame frequency location as the legacy PUCCH. For example, Slot 0 andSlot 1 may use different resource blocks and LL UEs may use either Slot0 or Slot 1.

According to certain aspects collisions on resources used to ACK uplinktransmissions may also be avoided by applying similar techniques aspresented above for preventing collision between QPUCCH and PUCCHresources.

Certain aspects of the present disclosure provide LL UL data channeltransmissions via QPUSCH and sounding reference signal (SRS)multiplexing. For example, the QPUSCH may be designed for slot leveltransmission with one DMRS symbol. For example, frequency tracking loopmay rely on either receiver implementation.

In certain aspects, QPUSCH may be designed to comprise 2 DMRS symbols,for example, by reusing the structure of PUCCH format 2. According tocertain aspects, a QPUSCH with 2 DRMS symbols may have to use ashortened pilot.

Additionally, according to certain aspects, for QPUSCH, slot hopping mayalso be allowed which may be conceptually similar to currentinter-subframe hopping.

According to certain aspects, for shortened format and SRStransmissions, PUSCH and PUCCH shortened formats may be supported toallow multiplexing with legacy transmissions. In some cases, SRStransmissions may be supported only in Slot 1.

Certain aspects of the present disclosure also provide for uplinkcontrol information (UCI) handling. For example, UCI may be sent onPUSCH to maintain single carrier-frequency division multiplexing(SC-FDM). Similar rules as legacy LTE design may be used to determinewhen to drop certain transmissions, for example, based on channelpriority. In addition, similar resource determination for LL UCI may beused on PUSCH. For example, a similar number of resources may be kept ifPUSCH assignment doubles in RBs with one slot assignment. In some cases,a new parameter (α⁻) may be used for ACK, rank indicator (RI), and CQIresource determination to allow for better optimization.

Certain aspects of the present disclosure provide methods formultiplexing CQI with slot-based PUSCH. For example, CQI may bemultiplexed on 1-slot PUSCH. In certain aspects, a 1 ms CQI may be usedwhen in fall back mode with 1 ms TTI.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software/firmwarecomponent(s) and/or module(s), including, but not limited to a circuit,an application specific integrated circuit (ASIC), or processor.Generally, where there are operations illustrated in the Figures (e.g.,FIGS. 7 and/or 8), those operations may be performed by any suitablecorresponding counterpart means plus function components. For example,means for providing, means for receiving, means fortransmitting/retransmitting, means for performing, means fordemodulating, means for allocating, means for determining, means forparticipating, and/or means for scheduling may comprise one or moretransmitters/receivers (e.g., TX/RX 618 and/or RX/TX 654) and/or one ormore processors (e.g., TX Processor 616/618, RX Processor 670/656,and/or Controller/Processor 675/658).

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an example of exemplary approaches. Based upondesign preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or combinations thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, software/firmware, or combinations thereof. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software/firmware dependsupon the particular application and design constraints imposed on theoverall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device (PLD), discretegate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in asoftware/firmware module executed by a processor, or in a combinationthereof. A software/firmware module may reside in RAM memory, flashmemory, PCM (phase change memory), ROM memory, EPROM memory, EEPROMmemory, registers, hard disk, a removable disk, a CD ROM, or any otherform of storage medium known in the art. An exemplary storage medium iscoupled to the processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium may be integral to the processor. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software/firmware, or combinations thereof. Ifimplemented in software, the functions may be stored on or transmittedover as one or more instructions or code on a computer-readable medium.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer-readable media may comprisenon-transitory computer-readable media (e.g., tangible media). Inaddition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, and any combination of any number of a, b, orc.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communications by a userequipment (UE), comprising: receiving, in a downlink subframe comprisingtwo slots, at least one type of advanced physical downlink controlchannel (aPDCCH) from a base station (BS); and demodulating the aPDCCHbased on a cell-specific reference signals (CRS).
 2. The method of claim1, wherein the aPDCCH occupies resources defined for demodulationreference signals (DMRS) in a legacy control channel when transmittingto certain types of UEs.
 3. The method of claim 1, wherein: the aPDCCHis transmitted in a control channel region that spans the two slots ofthe downlink subframe; the downlink subframe also comprises a datachannel region that spans the two slots of the downlink subframe forcarrying Machine Type Communication (MTC) data traffic; and the aPDCCHcomprises a quick physical downlink control channel (QPDCCH) having asingle-slot transmission time interval (TTI).
 4. An apparatus forwireless communications by a user equipment (UE), comprising: a memorycoupled with at least one processor, wherein the at least one processoris configured to: receive, in a downlink subframe comprising two slots,at least one type of advanced physical downlink control channel (aPDCCH)from a base station (BS); and demodulate the aPDCCH based on acell-specific reference signals (CRS).
 5. The apparatus of claim 4,wherein the aPDCCH occupies resources defined for demodulation referencesignals (DMRS) in a legacy control channel when transmitting to certaintypes of UEs.
 6. The apparatus of claim 4, wherein: the aPDCCH istransmitted in a control channel region that spans the two slots of thedownlink subframe; the downlink subframe also comprises a data channelregion that spans the two slots of the downlink subframe for carryingMachine Type Communication (MTC) data traffic; and the aPDCCH comprisesa quick physical downlink control channel (QPDCCH) having a single-slottransmission time interval (TTI).
 7. A non-transitory computer-readablemedium for wireless communications by a user equipment (UE), comprising:instructions that, when executed by at least one processor, configurethe at least one processor to: receive, in a downlink subframecomprising two slots, at least one type of advanced physical downlinkcontrol channel (aPDCCH) from a base station (BS); and demodulate theaPDCCH based on a cell-specific reference signals (CRS).
 8. Thenon-transitory computer-readable medium of claim 7, wherein the aPDCCHoccupies resources defined for demodulation reference signals (DMRS) ina legacy control channel when transmitting to certain types of UEs. 9.The non-transitory computer-readable medium of claim 7, wherein: theaPDCCH is transmitted in a control channel region that spans the twoslots of the downlink subframe; the downlink subframe also comprises adata channel region that spans the two slots of the downlink subframefor carrying Machine Type Communication (MTC) data traffic; and theaPDCCH comprises a quick physical downlink control channel (QPDCCH)having a single-slot transmission time interval (TTI).